Respiratory Syncytial Virus (RSV) is a common cold virus belonging to the family of paramyxovirus. RSV is virulent, easily transmissible and the most common cause of lower respiratory tract disease in children of less than 2 years of age. Up to 98% of children attending day care will be infected in a single RSV season. Between 0.5% and 3.2% of children with RSV infection require hospitalization. Approximately 90,000 hospital admissions and 4500 deaths per year were reported in United States. Major risk factors for hospitalization due to RSV are premature birth, chronic lung disease, congenital heart disease, compromised immunity, and age younger than 6 weeks in otherwise healthy children. No effective treatment of RSV positive bronchiolitis beside supportive care in the form of adequate nutrition and oxygen therapy is available. Antiviral therapies such as Ribavirin have not been proven to be effective in RSV infection. No vaccine is currently available for RSV prophylaxis.
The only RSV specific treatment available today is a humanized monoclonal antibody, palivizumab (also called SYNAGIS®), which is approved by the US Food and Drug Administration for the prevention of RSV lower respiratory disease in high-risk infants. However, palivizumab is not always effective. Another monoclonal antibody, motavizumab, also referred to herein as “mota”, was derived from palivizumab with enhanced antiviral activity. Both palivizumab and motavizumab bind antigenic site A, a highly conserved region on the RSV-F protein between amino acids 258 and 275. It is known that most anti-F antibodies, including palivizumab and motavizumab, recognize an epitope that is shared by the two conformations in which RSV-F can fold, the metastable pre-fusion form and the highly stable post-fusion conformation.
The present disclosure provides a conformational epitope on the pre-fusion conformation of RSV-F protein, recognized by a recently identified anti-RSV monoclonal antibody D25, disclosed in WO 2008/147196. By targeting the pre-fusion RSV-F structure, which is the active target for inhibition of RSV-F mediated fusion, the present disclosure also provides a method for screening more effective anti-RSV antibodies which are less susceptible to non-productive binding events, hence may provide better prevention or treatment for RSV infections.